18.40: Rahm Emanuel, the Mayor of Chicago and the former White House Chief of Staff, was among those who advised the President to water down his healthcare reforms and the focus instead on the economy. "Thank God for the country, he didn’t listen to me,” Emanuel says.

18.30: Romney's people are claiming they've raked in more than $1 million since the Supreme Court's ruling three hours ago. Here's the full footage of the Republican's comments.

18.20: Here's part of a little Q&A we did on the court's decision.

1. What does the law actually do?

The reforms are designed to expand health insurance to around 30 million of the 50 million Americans without coverage. The indvidual mandate forces everyone who can buy insurance to do so, pushing younger and healthier people into the market and hopefully driving down insurance premiums for all. The laws forbids insurance companies from discriminating against people with pre-existing health conditions and allows young people to stay on their parents' healthcare up to the age of 26. It also extends Medicaid, the government programme to provide health coverage to the very poor, although the court ruled that White House could not threaten states into accepting new Medicaid funding.

2. Why was the ruling by the Supreme court so important?

The court held the fate of millions of Americans, as well as Mr Obama's political legacy in its hands. Their decision means that "Obamacare", a landmark piece of legislation that will cost billions of dollars and affect lives for generations to come, will continue to be the law of land. Had they struck down the law they would have at a stroke erased one of the President's major domestic achievements and plunged the future of healthcare into enormous uncertainty.

3. What did it all come down to?

At the heart of the law is the "individual mandate" - a provision that forces all Americans who can afford health insurance to buy it. Conservatives argued that the mandate was unconstitutional because the government has no right to compel people to buy insurance. But the court made the surprise ruling that the mandate is a tax and therefore well within the powers of the federal government.

18.12: One last word on John Roberts. This is him messing up the oath of office on Obama's inauguration day. All is forgiven, John boy!

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17.55: It's difficult to overstate just how unexpected this outcome was. While politicos may now be busily deleting tweets the prevailing wisdowm was that Obamacare was on its way out. And it was going to be kicked out by Justice Kennedy, whose aggressive questions during the oral arguments earlier this year indicated that he was going to side with conservatives and tear down the individual mandate on the grounds that the government can't force people to engage in commerce.

Except it didn't happen like that. Kennedy sided with the conservatives but Chief Justice Roberts, once thought a hardline conservative, marched into the liberal camp. And while the court ruled that the individual mandate was not compatible with the Commerce Clause, it didn't matter because it decided that the mandate was a tax. Which, confusingly, was not an argument the Obama administration ever really made.

All of which is a long way of saying, Roberts has just become the most unlikely of liberal heroes (h/t David Weigel).

17.40: Today's ruling was undoubtedly a victory for Obama and the Democrats. But the Republicans can see a silver lining:

<noframe>Twitter: Ashley Parker - Team Romney believes that running against Obamacare will help revitalize the energy that helped sweep in R victories in 2010.</noframe>

Already the Republican National Committee is pushing out a memo saying: "The only way for voters to end [the ACA] and pursue true reform is to vote Republican in November."

17.35: As he often does, the President invoked a "real American" whose story had touched him. In this case it was Natoma Canfield who wrote to him when her insurance companies threatened to cut off her coverage.

I need your Health reform bill to help me!!! I simply can no longer afford to pay for my health care costs!! Thanks to this incredible premium increase demanded by my insurance company, January will be my last month of insurance.

17.25: Looking a bit tired but very pleased, Obama concludes:

Today I'm as confident as ever that we look back in five years, ten years, 15 years, we will be better off because we had the courage to pass this law and to keep moving forward.

17.17: Obama is speaking now from the same hallway where he announced the death ofOsama bin Laden. He says that those who are trying to score the court's decisions politically are "completely missing the point".

"Whatever the politics today's decision was victory for people all over the country whose life will now be more secure," he says. He's now rattling through the benefits of his reforms. He mentions that the "current Republican nominee" at one point supported the individual mandate.

17.04: We're expecting President Obama to speak at the White House in a few minutes.

16.55: Romney speaking across the the street from the Capitol now.

Let's be clear what the court did and did not do. It said Obamacare did not violate the consitution. It did not say it was a good law.

You can choose whether you want larger and larger government, more intrusive in your life, separating you and your doctor... or whether instead you want to return to a time when the American people made their own choices on healthcare.

16.45: We're expecting Mitt Romney to react to the court's ruling in just a moment.

16.23: The Republicans have a new battle cry: "Full repeal". Senate Minority leader Mitch McConnell just left the floor, vowing: "There's only one way to truly fix Obamacare. That's full repeal."

16.15: Reporting on dense legal decisions is a difficult skill and not one the cable networks have yet mastered. Here's CNN reporting that the law was struck down:

And then a few moments later reporting that it was in fact upheld:

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16.05: In the last few weeks the US has become a nation of Supreme Court anoraks, endlessly debating what the eyebrow twitches of Justice Kennedy meant and working out fantasy breakdowns for how the justices might rule. Here's the breakdown as it was announced in real life just over an hour ago:

15.56: And here's the non plain-English version. The full text of the Supreme Court's ruling on National Federation of Independent Businesses, et al v Sebelius, Secretary of Health and Human Services, et al:

15.52: Harry Reid, the Democrat Senate Majority Leader, has taken to the floor of the Senate to express as much joy as his little grey frame is capable of.

Passing the Affordable Care Act was the greatest single step in a generation in ensuring affordable care for all Americans... Our Supreme Court has spoken. The matter is settled...

15.45: The indispensable Scotus Blog offers this plain-English summary of what just happened:

The Affordable Care Act, including its individual mandate that virtually all Americans buy health insurance, is constitutional. There were not five votes to uphold it on the ground that Congress could use its power to regulate commerce between the states to require everyone to buy health insurance. However, five Justices agreed that the penalty that someone must pay if he refuses to buy insurance is a kind of tax that Congress can impose using its taxing power. That is all that matters.

Because the mandate survives, the Court did not need to decide what other parts of the statute were constitutional, except for a provision that required states to comply with new eligibility requirements for Medicaid or risk losing their funding. On that question, the Court held that the provision is constitutional as long as states would only lose new funds if they didn't comply with the new requirements, rather than all of their funding.

15:40: Here's an irony of political history: Senators Biden and Obama both voted against the confirmation of Chief Justice Roberts in 2005. Obama told the Senate that he didn't trust Roberts in those "five per cent of cases that are truly difficult".

15.36: Obama is due to speak from the White House within the next few hours but the Democratic crowing is beginning:

<noframe>Twitter: Nancy Pelosi - Victory for the American people! Millions of American families and children will have certainty of health care benefits + affordable care.</noframe>

15:30:Justice Kennedy actually wrote the dissenting opinion for the conservatives arguing that the entire law should be struck down, my colleague Charlie Whitfield reports.

In opening his statement in dissent, Kennedy says: "In our view, the entire Act before us is invalid in its entirety."

Kennedy, thought to be the potential swing vote and the least right-wing of the 5-justice conservative bloc, has instead written the most conservative dissent possible

President Obama's political legacy has been rescued by the one vote of Chief Justice Roberts.

15.27: Not that the Chief Justice is wild about the law. He notes pointedly in his opinion: "The court does not express any opinion on the wisdom of the [Affordable Care Act]"

15.22: Chief Justice John Roberts, a man appointed to America's high court by George W Bush, has voted to save Obama's healthcare plan. He joined in with the court's four more liberal justices to uphold the law. Justice Kennedy, the man who everyone thought would cast the deciding vote, is in the minority.

15.20: The word is filtering down to the crowds in front of the Supreme Court and the pro-Obama crowd are beginning to burst into uncertain cheers.

15.16: Here's the first verdict from Scotus Blog, the entire law is still standing except for a technical clause about the federal government's relationship with the states over Medicaid:

The bottom line: the entire ACA is upheld, with the exception that the federal government's power to terminate states' Medicaid funds is narrowly read.

15.15: This is very complicated and still unfolding but it sounds like the Supreme Court has ruled that the individual mandate is a tax, and the government has the right to levy taxes.

15.10: BREAKING: Scotus Blog, the definitive DC legal blog, is reporting that the mandate has been upheld and that Chief Justice Roberts has joined the liberal wing of the court.

Despite a turbulent month for Mr Obama, battered by disappointing jobs numbers and a high-profile Republican by-election victory in Wisconsin, the president was found to have established an eight-point lead in 12 key swing states, according to a poll by NBC and The Wall Street Journal.

The numbers, which were supported by the results of a Quinnipiac University poll, make grim reading for Mr Romney and contradict a widespread perception among political pundits of both stripes that the former Massachusetts governor had been gaining ground on Mr Obama.

15.05 Reports that Mr Obama will address the nation later today, after the verdict.

15.04 The Telegraph's US Editor Peter Foster writes:

President Obama, sitting in the Oval Office with Joe Biden, is facing the potential destruction of the major political achievement of his first term if the Supreme Court decides the Affordable Care Act is unconstitutional. The Obama legislative legacy is at stake as – Republicans will say – is the President’s credibility as a leader.

15.02 Underlining the size and scope of the decision, the nine Supreme Court justices held almost six hours of oral arguments over three days in late March, the longest time allotted to a single issue in more than 45 years. Paul Clement, who argued the case on behalf of the law's challengers, told reporters last week:

More people have paid attention to this case than any other case in recent memory, probably with the exception of Bush v Gore.

15.00 GMT (10.00 EDT) Hello and welcome to our live rolling coverage as Barack Obama faces two key verdicts: whether his landmark health care bill violated the constitution and whether his attorney general was in contempt of Congress over the 'Fast and Furious' scandal.